You aren't telling us if it is a buzz or a wheel-speed vibration but I'd bet, given the miles on the CD, it's wear in the driveshaft universal joint possibly coupled with bad/torn rubber in the center bearing support. The vibration occuring under acceleration and diminishing when the driveline is unloaded is the giveaway.

Give that center support a closer look...poke on it with a screwdriver. I'll bank that there's a tear in it somewhere.

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